I've experienced leaks are the most common. However I've installed new relays and actuators and tubing. One other thing to check at least annually is the filter (right of intake manifold) . Found mine slighty clogged that caused irratic operation. Anyone needing actuators, let me know, am rebuilding them for resale.

The most common reason for lazy eye is the seal on the front of the actuator. These seals are cheap and can be replaced fairly easily. I have found that it is easier to do it with the actuators off the car, but they can be done on the car, also. That's what it took to get mine working right, after replacing everything else.